1. Field of the Invention
The present invention relates to an improvement of a light source unit adopting light source arrays in a projection type image display device (projector) which is for modulating light beams of three primary colors in accordance with image information, synthesizing the modulated light beams to generate projection light and projecting an image onto a screen through a projection lens.
2. Description of the Related Art
In many conventional projection type image display devices, a discharge lamp such as a metal halide lamp or an ultra-high pressure mercury lamp is adopted as a light source for generating light beams of three primary colors. In case of using a so-called 3-CCD, white light emitted from a discharge lamp is separated into the three primary colors of red (R), green (G) and blue (B) by means of a dichroic mirror, and then the three primary colors are modulated in accordance with image information and synthesized by means of a synthesizing prism (dichroic prism), and thereafter, an image is displayed onto a screen through a projection lens.
To meet the demand for high luminance (high output) in such a projection type image display device using a discharge lamp, there has been made an attempt to adopt a discharge lamp of a high output or use multiple lamps. However, such an attempt results in an increase in the amount of heat generated from the discharge lamp, thus leading to an increase in size of a cooling structure. Measures for increasing the size of a noise preventing structure and that of a power supply, for example, also become essential. Moreover, since a light emission spectrum of the discharge lamp has a peak in yellow color, it is necessary to mix yellow color with red or green color for utilizing its output light effectively. Thus, there has been the problem that the resulting monochrome is poor in color purity and high color reproducibility cannot be attained. Further, in the discharge lamp, the quantity of light in the wavelength band of red color is not sufficient as compared with the quantity of light in the wavelength band of green color and that of blue color in a light emission spectrum, thus giving rise to the problem that it is necessary to take some measures for compensating the quantity of light in the wavelength band of red color.
As to the projection type image display device adopting the discharge lamp, despite the existence of the above-mentioned problems, there has been recently a growing demand for increasing the size of an image projected onto a screen, for example, in the business market and accordingly it is now the market's needs to increase the quantity of light. For solving the above-mentioned problems encountered in case of adopting the discharge lamp, attempts are being made to adopt a semiconductor laser array as a light source element intended for a high output (refer to Japanese Patent Laid-Open Publication No. 2007-201285).
The semiconductor laser array is, for example, an array of several ten or more monolithic semiconductor lasers arranged in high density on one and same semiconductor substrate, in which light emitting spots in a number corresponding to the arrayed number of semiconductor elements are formed. In case of adopting such a semiconductor laser array, it is an important subject to keep a set temperature for laser operation constant in order to ensure stable laser oscillation of each semiconductor laser in the semiconductor laser array.
If the set temperature for laser operation varies, the emission output from the semiconductor laser array varies, thus exerting an influence on the result of color synthesis and leading to shortening of the service life. In view of this point, according to the technique disclosed in Japanese Patent Laid-Open Publication No. 2007-201285, a Peltier device and a heat sink are combined to cool the semiconductor laser array. As another means for cooling the semiconductor laser array forcibly, there has been proposed means in which a coolant passage extending from a cooling device is disposed in parallel with the semiconductor laser array to cool the same array to a predetermined temperature (refer to Japanese Patent Laid-Open Publication No. 2005-026575).